JP2007098754A - Electrostatic actuator, liquid droplet ejection head and manufacturing method for them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable stable driving at a low voltage by suppressing a loss of electrostatic energy. <P>SOLUTION: In the electrostatic actuator which includes an elastically deformable and movable electrode member (diaphragm 22), a fixed electrode member (discrete electrode 31) arranged opposed to the movable electrode member via an insulating film 26 and a gap g, and a driving means (driving control circuit 4) which generates an electrostatic force between the movable electrode member and the fixed electrode member, a ratio of the surface roughness of the fixed electrode member and an apparent gap amount expressed by the following equation is made not larger than 0.15. Tm=Rm/(g+t/ε) wherein Tm is the ratio between the surface roughness of the fixed electrode member and the apparent gap amount, Rm is the surface roughness of the fixed electrode member, g is a gap amount, t is the thickness of the insulating film, and ε is a dielectric constant of the insulating film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrostatic actuator, a droplet discharge head, and a method for manufacturing the same, in which electrostatic energy is efficiently used in an electrostatic actuator driven by electrostatic force generated between opposing electrodes.

  2. Description of the Related Art An ink jet head mounted on a conventional ink jet printer is known that includes a so-called electrostatic drive type actuator (hereinafter referred to as an electrostatic actuator) that uses electrostatic force as a driving means. This electrostatic actuator includes, for example, an elastically deformable movable electrode member called a diaphragm that forms the bottom wall of the discharge chamber, and a fixed electrode called an individual electrode that is disposed opposite to the movable electrode member via an insulating film and a gap. And applying a driving voltage between these opposedly arranged diaphragms (movable electrode members) and individual electrodes (fixed electrode members) to generate electrostatic force. This is a driving method in which displacement is caused by electrostatic repulsion, and a part of ink in the ejection chamber is ejected as an ink droplet from a nozzle hole communicating with the ejection chamber by an internal pressure variation due to a change in volume of the ejection chamber accompanying this displacement.

In such an electrostatic actuator, when the diaphragm repeatedly contacts the individual electrode (fixed electrode member) with the insulating film interposed therebetween, contact charging occurs on the surface of the insulating film, and the contact charging causes the vibration of the diaphragm. There is a possibility that the electrostatic attraction force or the electrostatic repulsion force fluctuates and the vibration of the diaphragm becomes unstable. When the vibration of the diaphragm becomes unstable, ink droplets of an appropriate size are not ejected and unnecessary ink mist is generated. As a result, there are problems such as defective printing and ink stains on the ink nozzle surface and printer case.
Therefore, in order to solve such a problem, an ITO (Indium Tin Oxide) film is used as an individual electrode, and the surface of the ITO film is further provided with a plurality of protrusions smaller than the gap between the electrodes (for example, , See Patent Document 1). According to the electrostatic actuator of Patent Document 1, by providing such unevenness on the surface of the ITO film, the contact area is reduced when the diaphragm comes into contact with the individual electrode, and therefore the effect of reducing the amount of contact charging There is something.

JP 2001-10052 A (Page 4, FIGS. 1 and 4)

  However, if there are irregularities on the surface of the ITO film, the electrostatic energy decreases. Therefore, there is a problem that the input energy has to be increased in order to eject the ink satisfactorily. When the input voltage is increased, the voltage applied to the insulating film portion increases, and there is a risk that dielectric breakdown may occur. In addition, when the voltage is increased, the substance in the gap causes a polymerization reaction, and foreign matter is generated, which hinders driving of the head.

In view of the above problems, an object of the present invention is to provide an electrostatic actuator that can suppress loss of electrostatic energy and can be stably driven at a low voltage, and a method for manufacturing the same.
It is another object of the present invention to provide a droplet discharge head having such an electrostatic actuator and a method for manufacturing the same.

In order to solve the above-mentioned problems, an electrostatic actuator according to the present invention includes a movable electrode member that is elastically deformable, a fixed electrode member that is disposed opposite to the movable electrode member via an insulating film and a gap, and the movable electrode member. In an electrostatic actuator having a driving means for generating an electrostatic force between the fixed electrode member and the fixed electrode member,
It is considered that the surface roughness of the fixed electrode member represented by the following formula is a gap amount ratio of 0.15 or less.
Tm = Rm / (g + t / ε)
Here, Tm: Ratio of gap amount regarded as surface roughness of fixed electrode member
Rm: Surface roughness of the fixed electrode member
g: Gap amount
t: thickness of insulating film
ε: dielectric constant of insulating film

  As is apparent from the above formula, the electrostatic actuator of the present invention can suppress the loss of electrostatic energy by reducing the surface roughness of the fixed electrode member, and thus can be driven stably at a low voltage. Become. For example, when the gap is 100 nm and the surface roughness is 20 nm, the gap can be considered to be 100 nm by setting the gap design value to 120 nm. However, since the surface roughness cannot be controlled, the gap may be 120 nm. In that case, the drive voltage increases. When the width of the diaphragm is 50 μm, the thickness of the diaphragm is 1.0 μm, and the thickness of the insulating film is 0.1 μm, the drive voltage difference ΔV is 2V. By suppressing the surface roughness, this drive voltage difference can be reduced.

In the electrostatic actuator of the present invention, the fixed electrode member is formed of IZO or amorphous ITO or ITO whose surface is polished.
Since the fixed electrode member is made of IZO (Indium Zinc Oxide), amorphous ITO or ITO whose surface is polished, the surface roughness of the fixed electrode member can be reduced, so that the electrostatic energy Loss can be suppressed.

In the electrostatic actuator of the present invention, a hydrophobic film is formed on the surface of the insulating film facing the fixed electrode member.
If the surface roughness of the fixed electrode member is extremely reduced, when the movable electrode member repeats contact through the insulating film, there is a possibility that a sticking phenomenon may occur in which the fixed electrode member remains in contact with the fixed electrode member. In order to avoid such a sticking phenomenon, a hydrophobic film may be formed on the surface of the insulating film facing the fixed electrode member.
In this case, the hydrophobic film is preferably made of hexamethyldisilazane (HMDS).

  A droplet discharge head according to the present invention has any one of the electrostatic actuators described above. If the electrostatic actuator of the present invention is used for the droplet discharge head, the electrostatic energy can be efficiently used as described above, so that stable discharge performance can be exhibited with low voltage driving. In addition, since the gap amount is small, stable discharge performance can be exhibited.

  The method for manufacturing an electrostatic actuator according to the present invention includes a step of forming a recess in a substrate by etching, a step of forming an electrode material on the surface of the substrate including the recess to be thicker than a depth of the recess, A step of polishing the surface of the formed electrode film, a step of forming a fixed electrode member by patterning and etching a resist on the polished electrode film, and an electrode substrate on which the fixed electrode member is formed, And a step of bonding a silicon substrate having a movable electrode member through an insulating film and a gap.

  When commonly used polycrystalline ITO is used as the electrode material, for example, when the film is formed on the substrate surface by sputtering or the like, relatively large irregularities are formed on the surface of the electrode film. In order to reduce the surface roughness, a fixed electrode member having a small surface roughness can be formed by forming a film thicker than the depth of the recess during film formation, polishing the surface, and then patterning and etching the resist. can do.

  Further, the method for manufacturing an electrostatic actuator according to the present invention includes a step of forming a recess in the substrate by etching, and a step of forming an electrode material on the surface of the substrate including the recess to be thinner than the depth of the recess, A step of forming a fixed electrode member by patterning and etching a resist on the deposited electrode film, and silicon having a movable electrode member through an insulating film and a gap on the electrode substrate on which the fixed electrode member is formed And a step of bonding the substrates.

In this case, for example, amorphous ITO or IZO is used as the electrode material. These electrode materials have a surface roughness smaller than that of the polycrystalline ITO at the time of film formation, so it is not necessary to form a film thicker than the depth of the recess as described above, and the electrode material is formed thinner than the depth of the recess. do it. As a result, a desired gap can be secured, and the surface roughness can be reduced without polishing.
Moreover, you may further grind | polish the surface of the fixed electrode member after patterning as needed.

  In addition, as described above, in order to prevent the movable electrode member from sticking, it is also preferable to perform a hydrophobic treatment in which a hydrophobic film is formed on the surface of the insulating film facing the fixed electrode member.

The method for manufacturing a droplet discharge head according to the present invention is a method for manufacturing a droplet discharge head by any one of the above-described manufacturing methods.
As a result, it is possible to provide a liquid droplet ejection head having a stable ejection performance with low voltage driving.

  Hereinafter, embodiments of a droplet discharge head including an electrostatic actuator according to the present invention will be described with reference to the drawings. Here, as an example of a droplet discharge head, a face discharge type inkjet head that discharges ink droplets from nozzle holes provided on the surface of a nozzle substrate will be described with reference to FIGS. The present invention is not limited to the structure and shape shown in the following drawings, and can also be applied to an edge discharge type inkjet head that discharges ink droplets from nozzle holes provided at the end of a substrate. is there.

  FIG. 1 is an exploded perspective view showing an exploded schematic configuration of the ink jet head according to the present embodiment, and a part thereof is shown in cross section. FIG. 2 is a cross-sectional view of the ink jet head showing a schematic configuration in an assembled state. 1 and 2 are shown upside down from a state in which they are normally used.

  As shown in FIGS. 1 and 2, the inkjet head (an example of a droplet discharge head) 10 according to the present embodiment includes a nozzle substrate 1 in which a plurality of nozzle holes 11 are provided at a predetermined pitch, and each nozzle hole 11. On the other hand, the cavity substrate 2 provided with an ink supply path independently and the electrode substrate 3 provided with the individual electrodes 31 facing the diaphragm 22 of the cavity substrate 2 are bonded together.

  The electrostatic actuator according to the present embodiment includes the diaphragm 22 that is a movable electrode member that can be elastically deformed, and the individual electrode that is a fixed electrode member that is opposed to the diaphragm 22 via an insulating film 26 and a gap g. 31 and a drive control circuit (drive means) 4 that generates a static force by applying a drive voltage between the individual electrode 31 and the diaphragm 22. Hereinafter, the configuration of each substrate constituting the inkjet head 10 will be described.

The nozzle substrate 1 is made of, for example, a silicon single crystal substrate (hereinafter also simply referred to as a silicon substrate) having a thickness of 100 μm. A plurality of nozzle holes 11 are formed in the nozzle substrate 1. As shown in FIG. 2, each nozzle hole 11 has a cylindrical injection port portion 11 a perpendicular to the surface of the nozzle substrate 1 and an injection. There is provided an inlet portion 11b provided coaxially with the mouth portion 11a and having a larger diameter (or cross-sectional area) than that of the injection port portion 11a. Thus, by making the nozzle hole 11 have a two-stage hole, the ink droplet ejection direction can be aligned with the central axis direction of the nozzle hole 11, and stable ink ejection characteristics can be exhibited. That is, there is no variation in the flying direction of ink droplets, there is no scattering of ink droplets, and variations in the ejection amount of ink droplets can be suppressed.
Further, in FIG. 2 of the nozzle substrate 1, a narrow groove-like orifice 13 that forms a part of the ink flow path is provided on the lower surface (the surface on the bonding side with the cavity substrate 2).

  The cavity substrate 2 is made of, for example, a (110) plane silicon single crystal substrate having a thickness of about 140 μm (hereinafter, this substrate is also simply referred to as a silicon substrate). The silicon substrate is subjected to anisotropic wet etching to form recesses 24 and 25 for constituting the discharge chamber 21 and the reservoir 23 of the ink flow path. A plurality of recesses 24 are independently formed at positions corresponding to the nozzle holes 11. Therefore, as shown in FIG. 2, when the nozzle substrate 1 and the cavity substrate 2 are joined, each concave portion 24 constitutes a discharge chamber 21, communicates with each nozzle hole 11, and the orifice 13 that is an ink supply port. Both communicate with each other. The bottom wall of the discharge chamber 21 (recess 24) serves as the diaphragm 22. The diaphragm 22 can also be constituted by a boron doped layer formed by doping a silicon substrate with a high concentration of boron.

  The other recess 25 is for storing liquid material ink, and constitutes a common reservoir (common ink chamber) 23 for each discharge chamber 21. The reservoirs 23 (recesses 25) communicate with all the discharge chambers 21 through the orifices 13, respectively. Further, a hole penetrating the electrode substrate 3 described later is provided in the bottom of the reservoir 23, and ink is supplied from an ink cartridge (not shown) through the ink supply hole 34 of the hole.

  In addition, as described above, the silicon substrate having a (110) orientation is used as the cavity substrate 2 by performing anisotropic wet etching on the silicon substrate so that the side surfaces of the recesses and the grooves are formed on the upper surface of the silicon substrate. This is because the etching can be performed perpendicularly to the lower surface, whereby the density of the inkjet head can be increased.

An insulating film made of SiO ₂ or TEOS (Tetraethylorthosilicate Tetraethoxysilane) is formed on the entire surface of the cavity substrate 2 or at least the surface facing the electrode substrate 3 by thermal oxidation or plasma CVD (Chemical Vapor Deposition). 26 is applied with a film thickness of 0.1 μm. This insulating film 26 is provided for the purpose of preventing dielectric breakdown and short circuit when the ink jet head is driven.
On the upper surface of the cavity substrate 2, that is, the surface facing the nozzle plate 1 (including the inner surfaces of the discharge chamber 21 and the reservoir 23), an ink protection film (not shown) is similarly formed of a SiO ₂ film (including a TEOS film). This ink protective film is provided to prevent corrosion of the flow path by ink.

  The electrode substrate 3 is made from a glass substrate having a thickness of about 1 mm, for example. Among them, it is suitable to use a borosilicate heat-resistant hard glass having a thermal expansion coefficient close to that of the silicon substrate of the cavity substrate 2. This is because when the electrode substrate 3 and the cavity substrate 2 are anodically bonded, the thermal expansion coefficients of the two substrates are close to each other, so that the stress generated between the electrode substrate 3 and the cavity substrate 2 can be reduced. This is because the electrode substrate 3 and the cavity substrate 2 can be firmly bonded without causing the above problem. The electrode substrate 3 may be a silicon substrate made of the same material as the cavity substrate 2.

  The electrode substrate 3 is provided with a recess 32 at a position on the surface of the cavity substrate 2 facing each diaphragm 22. The recess 32 is formed to a depth of about 0.2 μm by etching. Each recess 32 is made of ITO (Indium Tin Oxide) or amorphous ITO or IZO (Indium Zinc Oxide) whose surface roughness is reduced by polishing or the like. The electrode 31 is formed by sputtering, for example, with a thickness of 0.1 μm. Therefore, the gap (gap) formed between the diaphragm 22 and the individual electrode 31 is determined by the depth of the recess 32 and the thickness of the insulating film 26 covering the individual electrode 31 and the diaphragm 22. This gap greatly affects the ejection characteristics of the inkjet head. In the above example, the gap g between the insulating film 26 on the lower surface of the diaphragm 22 and the individual electrode 31 after the cavity substrate 2 and the electrode substrate 3 are joined is 0.1 μm.

  The individual electrode 31 has a lead part 31a and a terminal part 31b connected to a flexible wiring board (not shown). The terminal portion 31b is exposed in the electrode extraction portion 35 where the end portion of the cavity substrate 2 is opened in order to facilitate connection of the flexible wiring board.

  As described above, the nozzle substrate 1, the cavity substrate 2, and the electrode substrate 3 are bonded to each other as shown in FIG. That is, the cavity substrate 2 and the electrode substrate 3 are generally bonded by anodic bonding, and the nozzle substrate 1 is bonded to the upper surface (the upper surface in FIG. 2) of the cavity substrate 2 by adhesion or the like. Further, a sealing through hole 28 for sealing the open end of the gap is formed in the rear end portion of the cavity substrate 2 by etching. For example, TEOS or the like is formed in the sealing through hole 28. A sealing portion 27 made of an epoxy adhesive or the like is formed. Thereby, moisture, dust and the like can be prevented from entering the gap, and the reliability of the inkjet head 10 can be kept high.

Finally, as shown in a simplified manner in FIGS. 1 and 2, a drive control circuit 4 such as an IC driver is provided with a common electrode (not shown) provided on the terminal portion 31 b of each individual electrode 31 and the cavity substrate 2. And the flexible wiring board (not shown).
Thus, the ink jet head 10 is completed.

Next, the operation of the inkjet head 10 configured as described above will be described.
The drive control circuit 4 is an oscillation circuit that controls the supply and stop of charges to the individual electrodes 31. This oscillation circuit oscillates at, for example, 24 kHz, and supplies electric charges by applying pulse potentials of, for example, 0 V and 30 V to the individual electrodes 31. When the oscillation circuit is driven and charges are supplied to the individual electrode 31 to be positively charged, the diaphragm 22 is negatively charged and an electrostatic force (Coulomb force) is generated between the individual electrode 31 and the diaphragm 22. Therefore, the diaphragm 22 is attracted to the individual electrode 31 by this electrostatic force and bends (displaces). As a result, the volume of the discharge chamber 21 increases. When the supply of electric charges to the individual electrode 31 is stopped, the diaphragm 22 returns to its original state due to its elastic force, and at this time, the volume of the discharge chamber 21 decreases rapidly. Part of the ink is ejected from the nozzle hole 11 as an ink droplet. Next, when the vibration plate 22 is similarly displaced, ink is supplied from the reservoir 23 to the discharge chamber 21 through the orifice 13.

Here, with reference to FIG. 3, the electrostatic energy which acts between the diaphragm 22 and the individual electrode 31 of this electrostatic actuator will be considered. FIG. 3 schematically shows the case where the surface roughness of the individual electrode 31 is present and not present. Therefore, the design gap amount (distance from the surface to the insulating film 26 when there is no surface roughness of the individual electrode 31) when designing the electrostatic actuator is actually reduced by the surface roughness. Yes.
If the surface roughness of the individual electrode 31 is Rm, the gap amount is g, the thickness of the insulating film 26 is t, and the dielectric constant of the insulating film 26 is ε, the electrostatic energy with and without the surface roughness is given. The ratio Er is expressed by the following equation (1).

  (G + t / ε) of the numerator of formula (1) corresponds to an amount called a deemed gap. Here, assuming that the ratio between the surface roughness and the gap amount is Tm, Tm can be expressed by Equation (2).

  At this time, the electrostatic energy ratio Er is as shown in FIG. 4 when Tm is considered as a variable. As can be seen from FIG. 4, as Tm increases, the electrostatic energy decreases compared to the case where there is no surface roughness. Therefore, in order to ensure 85% or more of electrostatic energy when there is no surface roughness, it is necessary to satisfy Tm ≦ 0.15.

  As described above, the electrostatic actuator according to the present embodiment reduces the surface roughness of the individual electrode 31 so that the ratio Tm between the surface roughness and the gap amount is 0.15 or less. As a result, stable driving at a low voltage is possible. That is, since an increase in voltage applied between the diaphragm 22 and the individual electrode 31 can be suppressed, the insulating film 26 does not cause dielectric breakdown, and a substance in the gap causes a polymerization reaction to generate foreign matter. Therefore, the ejection performance of the inkjet head can be kept stable for a long period of time.

Next, another embodiment of the electrostatic actuator of the present invention is shown in FIG. This figure is an enlarged cross-sectional view in the width direction of a certain electrostatic actuator section, and corresponds to the cross section taken along the line AA in FIG.
In the above-described embodiment, the surface roughness of the individual electrode 31 made of an ITO film or the like is reduced by polishing, but conversely, the diaphragm 22 is interposed between the individual electrode 31 via the insulating film 26. It may stick to and will not leave. When such a sticking of the diaphragm 22 occurs, the ink jet head 10 becomes inoperable. In this embodiment, means for preventing the sticking of the diaphragm 22 is taken. That is, the hydrophobic film 29 is formed on the surface of the insulating film 26 facing the individual electrode 31 by, for example, vapor phase processing. The hydrophobic film 29 is made of, for example, hexamethyldisilazane (HMDS). In this manner, the hydrophobic film 29 is formed on the surface of the insulating film 26 that faces the individual electrodes, whereby sticking of the diaphragm 22 can be prevented. Further, HMDS forming the hydrophobic film 29 has higher durability than PFDA (perfluorodecanoic acid), and since the constituent molecules are small, the hydrophobic film can be formed even in a narrow gap.

  Since the thickness of the hydrophobic film 29 is very thin compared to the thickness of the insulating film 26 and the individual electrode 31, the electrostatic energy ratio Er formula (1) and the surface roughness and the gap amount ratio Tm formula are shown. In (2), the thickness of the hydrophobic film 29 may be ignored.

  Next, an example of the manufacturing method of the electrode substrate in the electrostatic actuator of the present invention will be described with reference to FIG. 6 shows a longitudinal section of the electrostatic actuator, and the right figure shows a width section of the electrostatic actuator. Further, the thickness of the substrate and the etching depth in the following description are merely examples, and do not limit the present invention.

FIG. 6A shows a process of processing the recess 32 in the glass substrate 300. Here, a borosilicate glass substrate is used as the substrate material of the electrode substrate 3, and a glass substrate 300 processed to a predetermined thickness, for example, 1 mm is prepared. A silicon substrate can also be used as the substrate material. Then, an etching mask (not shown) made of chromium (Cr) is formed on the surface of the glass substrate 300 by sputtering, for example, and a resist (not shown) having a predetermined shape is patterned on the surface of the etching mask by photolithography. Etching is performed to form an opening having a shape corresponding to the recess 32 in the etching mask.
Next, the glass substrate 300 is etched with, for example, a hydrofluoric acid aqueous solution to form, for example, a recess 32 having a depth of 0.2 μm. Thereafter, after removing the resist with an organic stripping solution or the like, the glass substrate 300 is immersed in a chromium etching solution to remove the etching mask.

  FIG. 6B shows a step of forming an electrode material. Polycrystalline ITO is used as the electrode material. An ITO film 301 is formed as an electrode film on the entire surface of the glass substrate 300 including the recess 32 by sputtering the ITO, for example. The thickness of the ITO film 301 is, for example, 0.3 μm or more, and is thicker than the depth of the recess 32.

  FIG. 6C shows a polishing process of the ITO film 301. In this step, the surface of the ITO film 301 is polished by, for example, dry polishing or a back grinder. By this polishing process, the surface roughness of the ITO film 301 can be reduced. Further, the ITO film 301 is polished so that the thickness of the ITO film 301 remains thin on the surface of the glass substrate 300.

  FIG. 6D shows a process of patterning the polished ITO film 301. By patterning and etching a resist (not shown) by photolithography on the polished ITO film 301, an ITO pattern corresponding to the portion of the individual electrode 31 is formed.

  FIG. 6E shows a step of further polishing the individual electrode 31 made of an ITO film with an abrasive. In this step, the surface of the patterned ITO film (individual electrode 31) is polished by a mechanochemical reaction using an abrasive 303 called colloidal silica. As a result, the surface roughness of the individual electrode 31 can be further reduced. However, since this step has already been performed in the step (C), it is performed as necessary and may be omitted.

  Thus, the electrode substrate 3 on which the individual electrode 31 with reduced surface roughness is formed can be manufactured (FIG. 6F).

Here, the difference between the manufacturing method of the electrode substrate 3 of the present embodiment and the conventional manufacturing method of the electrode substrate 3 shown in FIG. 9 will be described.
In the conventional method, polycrystalline ITO, which is usually used as an electrode material, is used. When polycrystalline ITO is formed with a predetermined thickness (for example, 0.1 μm) by sputtering as shown in FIG. 9B, irregularities are formed on the surface thereof. Accordingly, as shown in FIG. 9C, the surface roughness of the ITO film (individual electrode 31) is relatively large even after patterning.
On the other hand, in this embodiment, even if the same polycrystalline ITO is used, the polycrystalline ITO film is formed thicker than the depth of the recess 32 as described above (FIG. 6B), and the surface of the ITO film is formed. After polishing (FIG. 6C), the surface roughness of the ITO film (individual electrode 31) is small even after patterning.

  Therefore, according to the manufacturing method of the electrode substrate 3 of the present embodiment, the surface roughness of the individual electrode 31 made of an ITO film can be reduced. Therefore, when this electrode substrate 3 is used as an electrostatic actuator, Electric energy can be used efficiently, and stable driving at a low voltage is possible.

  In addition, when amorphous ITO or IZO (Indium Zinc Oxide) is used as an electrode material instead of polycrystalline ITO, these materials have a smaller surface roughness after deposition than polycrystalline ITO. There is a nature to become. Therefore, if these materials are used, the electrode substrate 3 can be manufactured in the same process (see FIG. 9) as in the prior art, and the above-described processes in FIGS. 6B, 6C, and 6E are omitted. be able to. Note that the polishing step in FIG. 6E may be performed.

  Next, with reference to FIG. 7 and FIG. 8, an example of the manufacturing method of the inkjet head 10 of this embodiment is demonstrated roughly.

First, as shown in FIG. 7A, both sides of a (110) -oriented silicon substrate having a boron doped layer 201 are polished to prepare a silicon substrate 200 having a thickness of, for example, 525 μm.
Next, a TEOS film 202 serving as the insulating film 26 is formed to a thickness of 0.1 μm, for example, by plasma CVD over the entire lower surface of the boron doped layer 201 of the silicon substrate 200 (FIG. 7B). The TEOS film 202 is formed, for example, at a temperature of 360 ° C., a high frequency output of 250 W, a pressure of 66.7 Pa (0.5 Torr), a gas flow rate of TEOS flow rate of 100 cm ³ / min (100 sccm), and an oxygen flow rate of 1000 cm ³ / min (1000 sccm). Perform under the conditions of The insulating film 26 may be SiO ₂ .

Next, as shown in FIG. 7C, the electrode substrate 3 manufactured as shown in FIG. 6F and the silicon substrate 200 are anodically bonded through a TEOS film 202. The electrode substrate 3 is processed with a drill or the like so as not to penetrate the hole 304 serving as the ink supply hole 34 before bonding. This is because if the hole 304 is penetrated, the etching solution enters the gap g (see FIG. 2) in a later manufacturing process, and malfunction of the diaphragm 22 occurs. In addition, the TEOS film 202 is subjected to resist patterning on a portion to be the sealing through hole 28 and a portion to be the electrode extraction portion 35, and the TEOS film 202 at that portion is removed by etching.
In anodic bonding, the electrode substrate 3 and the silicon substrate 200 are heated to 360 ° C., a negative electrode is connected to the electrode substrate 3, and an anode is connected to the silicon substrate 200, and a voltage of 800 V is applied and bonded.

  Next, the anodic bonded silicon substrate 200 is thinned to a thickness of 140 μm by, for example, mechanical grinding or etching with an aqueous potassium hydroxide solution (FIG. 7D). Then, the work-affected layer formed on the surface of the silicon substrate 200 after mechanical grinding is removed by wet etching or the like.

  Next, a TEOS film (not shown) serving as an etching mask is formed on the entire surface of the bonded silicon substrate 200 by plasma CVD with a thickness of 1.5 μm, for example. Then, the TEOS film is provided with a recess 24 serving as the discharge chamber 21, a recess 25 serving as the reservoir 23, a recess 203 serving as the sealing through hole 28, and a recess 204 serving as the electrode extraction portion 35 (see FIG. 7E). The resist to be formed is patterned, and the TEOS films corresponding to the recesses are removed by etching, for example, with a buffered hydrofluoric acid solution.

Thereafter, the bonded silicon substrate 200 is wet-etched with a 35% by weight aqueous potassium hydroxide solution until the bottoms of the recesses 24, 25, 203, and 204 have a thickness of 10 μm. At this time, the etching of the portion of the recess 25 that becomes the reservoir 23 is delayed by half-etching the TEOS film.
Further, this bonded silicon substrate 200 is wet-etched with a 3% by weight potassium hydroxide aqueous solution, and the etching is continued until the etching stop by the boron doped layer 201 is sufficiently effective in each of the recesses 24, 25, 203, and 204 (FIG. 7). (E)). Here, the term “etching stop” refers to a state in which bubbles are not generated from the surface of the silicon substrate 200 to be etched, and etching is actually performed until bubbles are not generated.
As described above, the surface roughness of the diaphragm 22 formed by the bottom wall of the discharge chamber 21 can be suppressed to 0.05 μm or less by performing etching using two types of potassium hydroxide aqueous solutions having different concentrations. The ejection performance of the inkjet head 10 can be stabilized.

After the bonded silicon substrate 200 is etched, the silicon substrate 200 is etched with a hydrofluoric acid aqueous solution to remove the TEOS film formed on the silicon substrate 200. Thereafter, machining or laser processing is performed on the silicon substrate 200 to penetrate the hole 304 serving as the ink supply hole 34 to the recess 25 serving as the reservoir 23 (FIG. 8F).
Next, an ink protective film (not shown) made of TEOS is formed with a thickness of 0.1 μm, for example, by plasma CVD on the upper surface of the silicon substrate 200 on which the recesses 24 to be the discharge chambers 21 are formed. The film formation conditions of the ink protective film at this time are, for example, a temperature of 360 ° C., a high frequency output of 250 W, a pressure of 66.7 Pa (0.5 Torr), a TEOS flow rate of 100 cm ³ / min (100 sccm), and an oxygen flow rate of 1000 cm ³ / min (1000 sccm). ).

Next, a portion of the concave portion 203 that becomes the sealing through hole 28 of the silicon substrate 200 is processed by RIE (Reactive Ion Etching) dry etching to penetrate the sealing through hole 28, and at the same time, a concave portion that becomes the electrode extraction portion 35. The silicon substrate 200 in the portion 204 is removed to form the electrode extraction portion 35 (FIG. 8G). This RIE dry etching is performed for 60 minutes using a silicon mask under the conditions of an output of 200 W, a pressure of 40 Pa (0.3 Torr), and a CF ₄ flow rate of 30 cm ³ / min (30 sccm). Under this condition, the silicon substrate 200 in the recessed portion 203 serving as the sealing through-hole 28 and the recessed portion 204 serving as the electrode extraction portion 35 can be removed cleanly, causing damage to the individual electrode 31 made of ITO. It can etch without. Note that a CF-based gas other than CF ₄ can be used as the etching gas. In this RIE dry etching step, it is preferable to penetrate the sealing through hole 28 so that the opening of the insulating film 26 is narrower than the portion communicating with the gap g.

  Further, in order to prevent liquid such as water from entering the space of the gap g, for example, plasma CVD is performed from the sealing through hole 28 to form a sealing portion 27 made of TEOS to seal the space of the gap g ( FIG. 8 (H)). The sealing portion 27 may have a laminated structure of TEOS and aluminum oxide, for example. Thereby, aluminum oxide becomes a moisture permeation preventive layer, and the penetration of moisture can be effectively prevented.

  As described above, after the silicon substrate 200 is bonded to the electrode substrate 3 prepared in advance, the cavity substrate 2 as shown in FIGS. 1 and 2 can be manufactured. Therefore, even if the cavity substrate 2 is thinned, the electrode substrate 3 plays a reinforcing role as a support substrate, so that damage such as cracks or chipping of the cavity substrate 2 can be avoided, and handling properties are improved.

Then, the separately manufactured nozzle substrate 1 is bonded to the cavity substrate 2 with an epoxy adhesive (FIG. 8 (I)).
Finally, if the individual heads are separated by dicing, the ink jet head 10 shown in FIG. 2 is completed.

  Further, when the hydrophobic film 29 made of HMDS is formed on the insulating film 26 as shown in FIG. 4, the vapor phase treatment or liquid is performed at a stage before the step of forming the sealing portion 27 (FIG. 8H). Phase treatment is performed.

  As described above, according to the ink jet head manufacturing method of the present embodiment, the silicon substrate 200 is bonded to the electrode substrate 3 prepared in advance as described above, the silicon substrate 200 is thinned, and then discharged by etching. Since the cavity substrate 2 having recesses such as the chamber 21 and the reservoir 23 is manufactured, the cavity substrate 2 can be thinned without damaging the electrode substrate 3. Therefore, an inkjet head having a stable discharge performance by low voltage driving by efficiently using electrostatic energy can be obtained.

In the above embodiment, the electrostatic actuator, the inkjet head, and the manufacturing method thereof have been described. However, the present invention is not limited to the above embodiment, and various modifications can be made within the scope of the idea of the present invention. it can. For example, by changing the liquid material ejected from the nozzle holes, in addition to inkjet printers, the production of color filters for liquid crystal displays, the formation of light-emitting portions of organic EL display devices, the microarray of biomolecule solutions used for genetic testing, etc. It can be used as a droplet discharge device for various uses such as manufacture of
Moreover, although the diaphragm (movable electrode member) has been described as a thin plate type in which both ends are supported or a substantially rectangular entire circumference is fixed, a cantilever type may also be used. Further, the shape of the diaphragm is not particularly limited. For example, it may be circular, and an electrostatic actuator having a circular diaphragm can be used, for example, in a diaphragm portion of a micropump.

1 is an exploded perspective view showing a schematic configuration of an inkjet head according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an assembled state of the inkjet head of FIG. 1. Schematic sectional view of the electrostatic actuator with and without individual electrode surface roughness. The figure which shows the relationship between electrostatic energy ratio and surface roughness. The expanded sectional view of the width direction of the electrostatic actuator part which shows other embodiment of this invention. Sectional drawing of the manufacturing process which shows an example of the manufacturing method of the electrode substrate in the electrostatic actuator of this invention. Sectional drawing of the manufacturing process which shows an example of the manufacturing method of the inkjet head of this invention. Sectional drawing of the manufacturing process following FIG. Sectional drawing of the manufacturing process of the electrode substrate in the conventional electrostatic actuator.

Explanation of symbols

1 nozzle substrate, 2 cavity substrate, 3 electrode substrate, 4 drive control circuit, 10 inkjet head, 11 nozzle hole, 13 orifice, 21 discharge chamber, 22 diaphragm (movable electrode member), 23 reservoir, 26 insulating film, 27 sealing Stopping part, 28 Sealing through-hole, 29 Hydrophobic film, 31 Individual electrode (fixed electrode member), 32 Recessed part, 34 Ink supply hole, 35 Electrode extracting part, 200 Silicon substrate, 201 Boron doped layer, 202 TEOS film, 300 Glass Substrate, 301 ITO film, 303 abrasive.

Claims (12)

An elastically deformable movable electrode member, a fixed electrode member disposed opposite to the movable electrode member via an insulating film and a gap, and driving means for generating an electrostatic force between the movable electrode member and the fixed electrode member In an electrostatic actuator having
An electrostatic actuator represented by the following formula, wherein the fixed electrode member is regarded as having a surface roughness and a gap amount ratio is 0.15 or less.
Tm = Rm / (g + t / ε)
Here, Tm: Ratio of gap amount regarded as surface roughness of fixed electrode member
Rm: Surface roughness of the fixed electrode member
g: Gap amount
t: thickness of insulating film
ε: dielectric constant of insulating film   2. The electrostatic actuator according to claim 1, wherein the fixed electrode member is made of IZO, amorphous ITO, or polished ITO.   The electrostatic actuator according to claim 1, wherein a hydrophobic film is formed on a surface of the insulating film facing the fixed electrode member.   The electrostatic actuator according to claim 3, wherein the hydrophobic film is made of hexamethyldisilazane (HMDS).   A droplet discharge head comprising the electrostatic actuator according to claim 1. Forming a recess in the substrate by etching;
Depositing an electrode material on the surface of the substrate including the recesses thicker than the depth of the recesses;
Polishing the surface of the deposited electrode film;
Forming a fixed electrode member by patterning and etching a resist on the polished electrode film; and
Bonding a silicon substrate having a movable electrode member to an electrode substrate on which the fixed electrode member is formed via an insulating film and a gap;
A method for manufacturing an electrostatic actuator, comprising:   The method for manufacturing an electrostatic actuator according to claim 6, wherein the electrode material is polycrystalline ITO. Forming a recess in the substrate by etching;
Depositing an electrode material on the surface of the substrate including the recesses thinner than the depth of the recesses;
Forming a fixed electrode member by patterning and etching a resist on the deposited electrode film; and
Bonding a silicon substrate having a movable electrode member to an electrode substrate on which the fixed electrode member is formed via an insulating film and a gap;
A method for manufacturing an electrostatic actuator, comprising:   The method for manufacturing an electrostatic actuator according to claim 8, wherein the electrode material is amorphous ITO or IZO.   The method for manufacturing an electrostatic actuator according to claim 6, further comprising a step of polishing a surface of the fixed electrode member.   The method for manufacturing an electrostatic actuator according to claim 6, further comprising a step of performing a hydrophobic treatment to form a hydrophobic film on a surface of the insulating film facing the fixed electrode member. A method for manufacturing a droplet discharge head, wherein the droplet discharge head is manufactured by the manufacturing method according to claim 6.

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